A car bomb exploded in the rebel-held Syrian city of Idlib on Saturday, a war monitor and opposition news channel said, as air strikes hit its outskirts in a government offensive on the last major opposition bastion.

Syrian troops on Friday reclaimed a cluster of towns they had lost early in the eight-year-old war, pressing their offensive in the northwest, the country's last big rebel stronghold.

More than 70,000 people were displaced from the southern countryside of Idlib province in Syria during August due to a surge in violence, Idlib's health directorate said on Wednesday.

China's Syria envoy said Tuesday that "terrorist organisations" including the Islamic State group are being revived in the war-ravaged country, urging the international community not to ignore the "early warning" signs.

Regime air strikes on Saturday killed a woman and six of her children in northwest Syria, a war monitor said, a day after Russian bombardment pummelled a nearby displacement camp.

Militants on Wednesday downed a regime plane flying over northwest Syria as it took part in a deadly military campaign against the region and took the pilot prisoner

Syria's army has captured a strategically important town in Idlib in the rebels' last major enclave, a war monitor and a military media unit run by its ally Hezbollah reported on Sunday.

Regime loyalists captured a town and a village from militants and allied rebels in northwest Syria Wednesday, after fierce clashes that killed nearly 30 combatants overnight, a war monitor said.

Pro-government forces and opposition fighters exchanged fire in northwest Syria on Tuesday, killing seven civilians, a war monitor said, after Damascus scrapped a ceasefire.

Damascus resumed air strikes on northwest Syria Monday, a war monitor said, scrapping a ceasefire for the jihadist-run bastion and accusing rebels of targeting an airbase of its ally Russia.

A munitions blast killed 31 regime and allied fighters at a military airport in central Syria on Saturday, a war monitor said.

Air strikes on Syria's northwestern Idlib region stopped on Friday after the government announced it had agreed to a truce following more than three months of deadly bombardment.